public class MyLinkList1 {
    static class ListNode{
        private int val;//值域
        private ListNode prev;//前驱
        private ListNode next;//后继
        //构造方法
        public ListNode(int val){
            this.val = val;
        }
    }
    ListNode head = null;
    ListNode last = null;
   //获取链表长度
    public int size(){
        int length = 0;
        ListNode cur = head;
        while(cur != null){
            length++;
            cur = cur.next;
        }
        return length;
    }

    //打印链表
    public void display(){
        ListNode cur = head;
        while(cur != null){
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    //查找关键字key是否包含在链表中
    public boolean contains(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = null;
        }else {
            node.next = head;
            head.prev = node;
            head = node;
        }
    }

    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
        }else{
            node.prev = last;
            last.next = node;
            last = node;
        }
    }

    //在下标位置插入
    public void addIndex(int index,int data){
        ListNode node = new ListNode(data);
        if(index < 0 || index > size()){
            throw new RuntimeException(index+"下标错误，无法插入");
        }
        if(index == 0){
            addFirst(data);
            return;
        }
        if (index == size()){
            addLast(data);
            return;
        }
        //可以直接让cur走到index下标的位置
        int count = 0;
        ListNode cur = head;
        while (count != index){
            cur = cur.next;
            count++;
        }
        node.next = cur;
        node.prev = cur.prev;
        cur.prev.next = node;
        cur.prev = node;
    }

    //删除第一次值为key的元素
    public void remove(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
            //删除头节点
            if(cur == head){
                head = head.next;
                if(head != null){
                    head.prev = null;
                    }else{//只有一个节点的情况
                    last = null;
                    }
                }else{//删除中间和尾巴
                //删除尾巴
                if(cur.next==null){
                    cur.prev.next = cur.next;
                    last = last.prev;
                }else{//删除中间
                    cur.prev.next = cur.next;
                    cur.next.prev = cur.prev;
                    }
                }
            return;
            }else {
                cur = cur.next;
            }
        }
    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                //删除头结点
                if(cur == head){
                    head = head.next;
                    if(head != null) {
                        head.prev = null;
                    }else{//只有一个节点的情况
                        last = null;
                    }

                }else {//删除中间和尾巴
                    //删除尾巴
                    if(cur.next == null){
                        cur.prev.next = cur.next;
                        last = last.prev;

                    }else {//删除中间
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;

                    }
                }
            }
            cur = cur.next;
        }
    }
}
